The Whole Heliosphere Interval in the Context of a Long and Structured Solar Minimum: An Overview from Sun to Earth

Throughout months of extremely low solar activity during the recent extended solar-cycle minimum, structural evolution continued to be observed from the Sun through the solar wind and to the Earth. In 2008, the presence of long-lived and large low-latitude coronal holes meant that geospace was periodically impacted by high-speed streams, even though solar irradiance, activity, and interplanetary magnetic fields had reached levels as low as, or lower than, observed in past minima. This time period, which includes the first Whole Heliosphere Interval (WHI 1: Carrington Rotation (CR) 2068), illustrates the effects of fast solar-wind streams on the Earth in an otherwise quiet heliosphere. By the end of 2008, sunspots and solar irradiance had reached their lowest levels for this minimum (e.g., WHI 2: CR 2078), and continued solar magnetic-flux evolution had led to a flattening of the heliospheric current sheet and the decay of the low-latitude coronal holes and associated Earth-intersecting high-speed solar-wind streams. As the new solar cycle slowly began, solar-wind and geospace observables stayed low or continued to decline, reaching very low levels by June??C?July 2009. At this point (e.g., WHI 3: CR 2085) the Sun?CEarth system, taken as a whole, was at its quietest. In this article we present an overview of observations that span the period 2008??C?2009, with highlighted discussion of CRs 2068, 2078, and 2085. We show side-by-side observables from the Sun??s interior through its surface and atmosphere, through the solar wind and heliosphere and to the Earth??s space environment and upper atmosphere, and reference detailed studies of these various regimes within this topical issue and elsewhere.     

Coronal holes as sources of solar wind

We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial coronal holes seen during the Skylab period were associated with high-velocity solar wind streams observed at 1 AU.Harvard College Observatory-Smithsonian Astrophysical Observatory.A substantial portion of this work was done while a visiting scientist at American Science and Engineering.     

A new model for flux emergence and the evolution of sunspots and the large-scale fields

Existing models for the evolution of sunspots and sunspot groups, describing the subsurface structure of the magnetic fields and their interactions with the convective motions, are briefly reviewed. It is shown that they are generally unable to account for the most recent data concerning the relationship between the large-scale solar magnetic field structures and the magnetic fields of active regions. In particular, it is shown that the former do not arise directly from the decay of the latter, as required by the Babcock model and all other models based on it. Other observations which are not adequately explained by current models are also cited.A new model is put forward based on the expulsion of toroidal magnetic flux by the dominant (i.e. giant) cells of the convection zone. The flux expelled above these cells forms the large-scale field and thus the configuration of this field provides a clue to the structure of the giant cell patterns. The flux expelled below the cells becomes twisted into a rope as in the Babcock model but a loop or stitch forms only in the region of upflow of the giant cells. The interaction of this loop with intermediate-sized cells as it rises to the surface determines the configuration and extent of the active region which appears at the surface. The compatibility of the model with other observations is discussed and its implications for theories of the solar cycle are noted.     

<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of the eruptive history of Mount Erebus,Antarctica: summit flows,tephra, and caldera collapse

Eruptive activity has occurred in the summit region of Mount Erebus over the last 95 ky, and has included numerous lava flows and small explosive eruptions, at least one plinian eruption, and at least one and probably two caldera-forming events. Furnace and laser step-heating ⁴⁰Ar/³⁹Ar ages have been determined for 16 summit lava flows and three englacial tephra layers erupted from Mount Erebus. The summit region is composed of at least one or possibly two superimposed calderas that have been filled by post-caldera lava flows ranging in age from 17 ± 8 to 1 ± 5 ka. Dated pre-caldera summit flows display two age populations at 95 ± 9 to 76 ± 4 ka and 27 ± 3 to 21 ± 4 ka of samples with tephriphonolite and phonolite compositions, respectively. A caldera-collapse event occurred between 25 and 11 ka. An older caldera-collapse event is likely to have occurred between 80 and 24 ka. Two englacial tephra layers from the flanks of Mount Erebus have been dated at 71 ± 5 and 15 ± 4 ka. These layers stratigraphically bracket 14 undated tephra layers, and predate 19 undated tephra layers, indicating that small-scale explosive activity has occurred throughout the late Pleistocene and Holocene eruptive history of Mount Erebus. A distal, englacial plinian-fall tephra sample has an age of 39 ± 6 ka and may have been associated with the older of the two caldera-collapse events. A shift in magma composition from tephriphonolite to phonolite occurred at around 36 ka.Editorial responsibility: Julie Donnelly-Nolan     

Hydrochemistry of formation water with implication to diagenetic reactions in Sanzhao depression and Qijia-gulong depression of Songliao Basin, China

The Sanzhao depression and Qijia-gulong depression are two of the most important hydrocarbon-bearing sub-depressions in the Songliao basin, dominated by Cretaceous fluvial and lacustrine strata with volcanic and volcaniclastic rocks. In this paper, the pressure distributions and hydrochemistry variations in those two depressions are investigated. It is found that the Qijia-gulong depression is dominated by overpressure, but the Sanzhao depression is dominated by underpressure, especially in the Quantou formation. The salinity of formation water ranges from 1.0 g/L to 20 g/L, with a mean of 4 g/L in most formations. Water composition is dominated by NaHCO₃ water type but varies greatly in salinity and ionic ratios in the different depressions. The results of mass balance calculation reveal that, fluid chemistry in the Qijia-gulong depression is dominated by dissolution of silicate minerals and halite, whereas in the Sanzhao depression it is dominated by silicate mineral dissolution, evaporite dissolution (halite and gypsum), carbonate mineral dissolution/precipitation, and cation exchange.     

Crustal-scale seismic profiles across Taiwan and the western Philippine Sea

We have used combined onshore and offshore wide-angle seismic data sets to model the velocity structure of the Taiwan arc–continent collision along three cross-island transects. Although Taiwan is well known as a collisional orogen, relatively few data have been collected that reveal the deeper structure resulting from this lithospheric-scale process. Our southern transect crosses the Hengchun Peninsula of southernmost Taiwan and demonstrates characteristics of incipient collision. Here, 11-km-thick, transitional crust of the Eurasian plate (EUP) subducts beneath a large, rapidly growing accretionary prism. This prism also overrides the N. Luzon forearc to the east as it grows. Just west of the arc axis there is an abrupt discontinuity in the forearc velocity structure. Because this break is accompanied by intense seismicity, we interpret that the forearc block is being detached from the N. Luzon arc and Philippine Sea plate (PSP) at this point. Our middle transect illustrates the structure of the developing collision. Steep and overturned velocity contours indicate probable large-scale thrust boundaries across the orogen. The leading edge of the coherent PSP appears to extend to beneath the east coast of Taiwan. Deformation of the PSP is largely limited to the remnant N. Luzon arc with no evidence of crustal thickening to the east in the Huatung basin. Our northern transect illustrates slab–continent collision—the continuing collision of the PSP and EUP as the PSP subducts. The collisional contact is below 20 km depths along this transect NE of Hualien. This transect shows elements of the transition from arc–continent collision to Ryukyu arc subduction. Both of our models across the Central Range suggest that the Paleozoic to Mesozoic basement rocks there may have been emplaced as thick, coherent thrust sheets. This suggests a process of partial continental subduction followed by intra-crustal detachment and buoyancy-aided exhumation. Although our models provide previously unknown structural information about the Taiwan orogen, our data do not define the deepest orogenic structure nor the structure of western Taiwan. Additional seismic (active and passive), geologic, and geodynamic modeling work must be done to fully define the structure, the active deformation zones, and the key geodynamic process of the Taiwan arc–continent collision.     

Pleistocene recharge to midcontinent basins: effects on salinity structure and microbial gas generation

The hydrogeochemistry of saline-meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history, chemical evolution of basinal brines, and physical stability of saline formation waters during episodes of freshwater recharge. This is especially germane for interior cratonic basins, such as the Michigan and Illinois basins. Although there are large differences in formation water salinity and hydrostratigraphy in these basins, both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the Pleistocene. Exploration for unconventional microbial gas deposits, which began in the upper Devonian-age Antrim Shale at the northern margin of the Michigan Basin, has recently extended into the age-equivalent New Albany Shale of the neighboring Illinois Basin, providing access to heretofore unavailable fluid samples. These reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry.New-formation water and gas samples were obtained from Devonian-Mississippian strata in the Illinois Basin. These included exploration wells in the New Albany Shale, an organic-rich black shale of upper Devonian age, and formation waters from over- and underlying regional aquifer systems (Siluro-Devonian and Mississippian age). The hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the Illinois Basin critically influenced fluid migration into the New Albany Shale. The New Albany Shale formation water chemistry indicates significant invasion of meteoric water, with δD values as low as −46.05‰, into the shale. The carbon stable isotope system (δ¹³C values as high as 29.4‰), coupled with δ¹⁸O, δD, and alkalinity of formation waters (alkalinity ≤24.08 meq/kg), identifies the presence of microbial gas associated with meteoric recharge. Regional geochemical patterns identify the underlying Siluro-Devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured New Albany Shale reservoirs. Recharge from overlying Mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the New Albany Shale.Recharge of dilute waters (Cl⁻ <1000 mM) into the Siluro-Devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern Illinois Basin margin. Taken together with salinity and stable isotope patterns in age-equivalent Michigan Basin formation waters, they suggest a regional impact of recharge of δ¹⁸O- and δD-depleted fluids related to Pleistocene glaciation. Devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane. This recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity. Given the relatively quiet tectonic history and subdued current topography in the midcontinent region, it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale-hosted gas deposits.     

Type III radio burst productivity of solar flares

We study the statistical relationship between type III radio bursts and optical flares, using the comprehensive flare data base at the NOAA National Geophysical Data Center (Boulder, Colorado), and the radio observations obtained with the ARTEMIS multichannel spectrograph in Nancay (France), operating at 500–100 MHz.At variance with previous results, we find that type III probability of occurrence depends only weakly upon the spatial extension of the flare observed in H, but strongly upon its brightness. We also confirm that type III probability increases with proximity to sunspots and with mass motions (surges and prominence activity); in addition, our statistical data are consistent with both relations holding at fixed flare brightness. Thus, some of the conditions favorable to type III occurrence are characteristic of compact flares, while others are characteristic of large and long-duration flares, which are often related to mass ejections. This apparent paradox suggests that particle acceleration and magnetic expansion are at work simultaneously in the ejection of electron streams out of flaring sites.     

The effect of supplementary dietary copper on copper and metallothionein levels in the fish, dab, Limanda limanda

Common dab were fed a casein based diet containing copper at a concentration of 1·4 mg copper kg⁻¹ (dry weight) or a similar diet supplemented with 200 mg copper kg⁻¹. Fish were sampled after 10 weeks and 20 weeks and hepatic and renal copper, zinc and metallothionein concentrations were measured. All hepatic cytosolic copper in test and control fish co-eluted from Sephadex G-75 with metallothionein, as did some of the cytosolic zinc. After 20 weeks there was three times as much of this metallothionein-bound copper in the livers of the test fish compared to the control fish, although metallothionein concentration was little elevated. On the basis of these results it is proposed that cytosolic liver copper concentration or heat stable liver copper concentration can be used as an indication of excess dietary copper in the dab Limanda limanda.